Inner Primary Crack and Leak

swooshdave · Sep 26, 2020

The one nice thing about Royal Purple is you know when it’s engine oil leaking.

So I noticed some purple oil coming out the left side of the engine. Belt drive so maybe the seal has blown? Then I spot what appears to be a slight gap at the front. And what looks like a crack. Maybe I didn’t shim it right and I’ve pulled one of the mounting bolts loose?

Took it all apart. Tried to not cry at all the fresh engine oil getting drained. Shocking how much oil gets in the crankcase when they wet sump.

I must have misjudged the amount of shimming I needed? I’m sure I checked it. What’s your favorite tricks for checking this?

Because the primary is dry I’m not too concerned with the crack. I’m just going to get a new gasket and some shims. And do a better job of sealing around the bolt holes.

gortnipper · Sep 26, 2020

Dry bolt it on with the three bolts and without a shim and use a feeler guage to figure out how thick.

And or vice versa.

It looks like that corner is lower on the case to pull in like that, so you may want to check things with a straight edge on the case and on the inner cover.

Clean out the crack with meths and smear some JB in the cracks to seal before you put back for good measure.

grandpaul · Sep 26, 2020

Very typical of improper shimming and/or overtightening. JB Weld or proper weld repair, then carefully shim properly (kinda hard to measure exactly, but if you get to within .010" it will flex without cracking.

swooshdave · Oct 2, 2020

I’m starting to wonder if it was cracked previously. I think the leaking was because I didn’t seal around the bolt holes properly.

I rechecked the distance and it was really close to the washer I had in there. My caliper died so I can’t give you exact measurements but I’d guess with the washer it was less than .010”.

Hopefully I can start it up today and I put everything back together correctly.

maylar · Oct 2, 2020

Do that with the gasket in place, of course.
BTW I would have that crack welded, and not trust epoxy.

jbruney · Oct 2, 2020

swooshdave · Oct 2, 2020

The primary is dry so I'm going to leave it for now. Since that area should be in compression I don't see any ill effects from leaving it. Thoughts?

Derek Wilson · Oct 2, 2020

swooshdave said:
I’m starting to wonder if it was cracked previously. I think the leaking was because I didn’t seal around the bolt holes properly.

I rechecked the distance and it was really close to the washer I had in there. My caliper died so I can’t give you exact measurements but I’d guess with the washer it was less than .010”.

Hopefully I can start it up today and I put everything back together correctly.

Check the gap with some feeler gauges. That looks like more than 0.010" to me, more like 0.020" to 0.030", and more if you run a gasket. I have been using sealing compound (per Alton, don't see why you couldn't do with the stock set up if proper shimmed)

I would leave the crack be, just get the shims right so that it is not put under any extra stress.

FWIW

swooshdave · Oct 2, 2020

Derek Wilson said:
Check the gap with some feeler gauges. That looks like more than 0.010" to me, more like 0.020" to 0.030", and more if you run a gasket. I have been using sealing compound (per Alton, don't see why you couldn't do with the stock set up if proper shimmed)

I would leave the crack be, just get the shims right so that it is not put under any extra stress.

FWIW

What I said is with the washer that was in there (not shown in this picture) the gap was more like .010". I should have been more clear.

Onder · Oct 3, 2020

I looked at AN for a price on a new inner. 120 quid for you plus VAT for us. Not bad in my opinion. Now I am fully aware that you are not worried about leaks but unless you have a local welder who is good and not too expensive might it not be better to remove future worries and go new or even find one on ebay? Most of us of a certain age have learned doing it right the first time usually pays.

SteveC · Oct 3, 2020

My vote - get it welded. Probably cost less than you think.

I had some cracks in my Trident inner case welded that were causing an oil leak into the dry clutch. Only cost me 25 UK pounds and took the welder all of 5minutes to weld. Biggest hassle is thoroughly degreasing the cracks. The welds were easily dressed with a flap disc thingy.

Seeley920 · Oct 3, 2020

You're running a belt?

Just make sure the threads in the crankcase are good, as that has to be where your oil is coming from. Use blue loctite when you reassemble. The crack is pretty much irrelevant to oil leaks

milfordite · Oct 3, 2020

What I do now days is to chuck up the standoff in the lathe and cut back the solid part. Then extend the threads so that you can add a locknut. Thread the locknut down until the length is just right and then tighten the nut on the inside of the cradle. No shims needed, similar to how the MKIII inner case is installed. I'd post a photo but have never figured that part out since I don't use a photo host site.

jbruney · Oct 3, 2020

When rebuilding my clutch/replacing sprocket last winter mine had quite the gap as it was loosened, but no cracks to worry about migrating further. I found the existing shim(s) accompanied by an 1/4" SAE 304 SS flat washer to set thing perfectly upon installation. This also alleviated the drive chain connector link from gradually wearing into the backside inner primary cover... An issue I can thank the 1st PO for because the 2nd didn't have her long enough to go on adventures.
I know I hooted & hollered weld but I concur, with it being dry if cracks don't grow then to hell with further pursuit. Just don't scratch it because I'll surely weep. That's got to be.......... 'Ole Yeller".

swooshdave · Oct 3, 2020

Seeley920 said:
You're running a belt?

Just make sure the threads in the crankcase are good, as that has to be where your oil is coming from. Use blue loctite when you reassemble. The crack is pretty much irrelevant to oil leaks

These had helicoils. Was that standard?

kommando · Oct 3, 2020

swooshdave said:
These had helicoils. Was that standard?

Yes, on my 70, 72 and 74 crankcases.

Fast Eddie · Oct 3, 2020

milfordite said:
What I do now days is to chuck up the standoff in the lathe and cut back the solid part. Then extend the threads so that you can add a locknut. Thread the locknut down until the length is just right and then tighten the nut on the inside of the cradle. No shims needed, similar to how the MKIII inner case is installed. I'd post a photo but have never figured that part out since I don't use a photo host site.

That‘s how they shudda been !

Inner Primary Crack and Leak

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